This invention is concerned with a plunger mechanism for use in a glassware forming machine, the mechanism being for use in moving a plunger into or out of a mould cavity of a mould of the machine. Such plunger mechanisms are used, for example, in glassware forming machines of the individual section type and also in other types of machine.
Glassware forming machines of the individual section type are well-known. These machines comprise a number of individual forming units, called "sections", which all receive gobs of molten glass from a common source and feed their output to a common conveyor. Each section comprises at least one parison-forming mould in which gobs of molten glass are formed into parisons and at least one blow mould in which the parisons are blown to the required shape. Parisons are formed in a mould cavity of a parison-forming mould of a machine of the individual section type either by a pressing operation or by a blowing operation.
A conventional plunger mechanism comprises a cylinder disposed below the parison mould, and a piston movable in the cylinder towards or away from the mould cavity upon the introduction of fluid under pressure into the cylinder. A piston rod projects from the piston towards the mould cavity and is arranged to carry a plunger so that movement of the piston causes movement of the plunger towards or away from the mould cavity. In a press-and-blow process in which the parison is formed by a pressing operation and the parison is subsequently blown, the piston is moved by air pressure to move the plunger into the mould cavity so that the plunger presses the glass to the shape of the cavity. Air under pressure is then used to move the plunger fully out of the mould cavity to allow the parison to be removed. Finally, the plunger is moved to an intermediate position, either by a spring compressed as the plunger was withdrawn from the cavity or by an auxiliary piston and cylinder assembly, and the next gob of molten glass is introduced into the mould cavity on top of the plunger. In a blow-and-blow process in which the parison is formed by the blowing operation and the parison is subsequently blown again, the plunger is directly mounted on the piston rod and is surrounded by a thimble which is spring urged towards the mould cavity. A further spring acts between the thimble and the piston rod. In operation, air pressure urges the plunger into the mould cavity into a load position in which a gob of molten glass is dropped on top of the plunger. The air pressure is then removed and the further spring aforementioned moves the plunger away from the mould cavity to a counter-blow position in which air can be blown past the plunger into the mould cavity to cause a parison to be formed therein. Air pressure is then used to pull the plunger and the thimble away from the mould cavity, compressing both springs. This brings the plunger to a position in which it is clear of the mould cavity so that the parison can be removed.
In the press-and-blow process, since the plunger of a plunger mechanism contacts molten glass, it requires cooling to prevent it from becoming so hot that it sticks to the glass and cannot be successfully withdrawn therefrom. Conventionally, this cooling is provided by cooling air which passes through a passage passing centrally through the piston and the piston rod, the passage being arranged to communicate with a chamber within the plunger so that the cooling air can pass into the chamber. A tube extends through the cylinder into the passage, the tube being fixed against movement with the piston and the piston rod. The tube is arranged to be connected to a source of air under pressure so as to supply cooling air to the passage. In the blow-and-blow process, this tube supplies the air for blowing a parison or is connected to a source of vacuum to suck air from the mould cavity. Since the tube passes through the piston, it is necessary that the gap between the wall of the passage be sealed to enable the piston to be moved effectively. This seal has to be able to operate over a long period of time and, because the cooling tube may be utilised to connect the mould cavity to a vacuum source when the parison is formed by a blowing operation, has to be able to resist damage from hot gases or glass particles passing along the passage. A conventional sealing means arranged to seal the gap between the exterior of the tube and the wall of the passage uses reinforced polytetrafluorethylene rings which are v-shaped in transverse cross-section. For example, six rings are used with three facing in each direction and these rings are mainained in compression by means of a coil spring. This sealing means is expensive, is a source of considerable friction, and occupies a considerable space.
It is an object of the present invention to provide a plunger mechanism comprising sealing means which is less expensive, cause less friction, and is more compact than the above-mentioned conventional sealing means.